Photographic products, processes, and compositions



United States Patent 3,019,104 PHOTOGRAPHIC PRODUCTS, PROCESSES, ANDCOMPOSITIONS Gerald Oster, Brooklyn, N.Y., assignor to PolaroidCorporation, Cambridge, Mass, a corporation of Delaware No Drawing.Filed Dec. 11, 1957, Ser. No. 701,991 9 Claims. (Cl. 96-29) The presentinvention is concerned with photography and more particularly withphotographic products and processes for producing photographic imageshaving increased density.

One object of this invention is to provide processes for producingphotographic images having increased density.

Another object of this invention is to provide novel photographicproducts embodying the means for increasing the density of aphotographic image.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the several steps and the relationand order of one or more of such steps with respect to each of theothers, and the product possessing the features, properties and therelation of elements which are exemplified in the following detaileddisclosure, and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description.

When a photographic emulsion is exposed to light, or other form ofradiant energy, the grains of silver halide in the exposed areas arerendered developable and, upon development, are reduced to metallicsilver. The density of the resulting images, in general, is dependentupon the number of grains of silver produced, the size of the grains,and the interspatial distance between said grains.

I have discovered that photographic images, having increased density,may be produced by carrying out the development in the presence of apolymerizable vinyl monomer and causing said monomer to be polymerizedduring the development step. Apparently, the polymer, produced, servesto bind the exposed and developed crystals which thereby exhibit a verydense image since light scattering per unit weight of developed silveris considerably decreased on aggregation of the grains.

In carrying out the processes of this invention a latent silver halideimage is developed with a developing agent which, upon oxidation, passesthrough a free radical state. The free radicals, produced a intermediateoxidation products of the developing agent during the development, areused to initiate and propagate the polymerization of the vinyl monomer.The areas of polymerization will be substantially coextensive with theareas in which reduction of silver halide and oxidation of thedeveloping agent are taking place (i.e., the exposed areas) and little,if any, polymer will be produced in unexposed areas. A group ofdevelopers, which pass through a free radical state upon being oxidizedand which are especially useful in carrying out the processes of thisinvention, are those of the benzenoid class. In general, developingagents of this class contain an aryl nucleus substituted in the orthoand para positions, with respect to each other, by hydroxyl and/ oramino groups, including alkyl and aryl substituted amino groups. Thearyl nucleus in such developers may also be further substituted by othersubstituents such, for example, as alkyl, aryl, alkoxy, etc., groups. Asexamples of benzenoid developing agents which are useful in carrying outthe processes of this invention, mention may be made of p-aminophenolhydrochloride, 2-a1nino-5-diethylaminotoluene hydrochloride,p-toluhydroquinone, p-methylaminophenol sulfate, hydroquinone diaceticacid, 3,5 -'dimethyl-4-aminophenol, p-benzylaminophenol, 2,6-dimethyl-4aminophenol, 4-amino-1-naphthol hydrochloride,2,5-dimethyl-4-aminophenol, 4-anilinophenol, 4-amino-2-methoxy-phenoland p-phenylene diamine.

Since the life cycle of the free radicals, produced during development,is generally of short duration, the vinyl monomer must be present at thetime of development. It has been found that no increase in density orpolymerization will occur if the monomer is added after development. Ina preferred mode of carrying out the processes of this invention, thevinyl monomer is incorporated in the photosensitive emulsion prior toexposure. This may be readily accomplished, for example, by dissolvingor emulsifying the monomer in the silver halide: emulsion coatingsolution prior to its application to a suitable support. In certaininstances the developing agent may be incorporated along with the vinylmonomer into the photosensitive element prior to exposure. In such anembodiment the developing agent may be rendered operative after exposureby permeating the photosensitive element with an aqueous alkalinesolution. In another useful mode of carrying out the invention, themonomer is incorporated in the developing solution and imbibed on thephotosensitive emulsion along with the developing agent.

Monomers suitable for use in the processes herein disclosed may beselected from any of the polymerizable vinyl monomers available. It willbe understood that the especially useful monomers are those which arereadily dissolved or emulsified in the photosensitive emulsion ordeveloping solution. A preferred class of monomers are the salts ofvinyl acids. Such monomers have low vapor pressures, and thus thephotosensitive elements in which they are incorporated will haveconsiderably longer shelf lives. The amount of vinyl monomerincorporated will depend upon the amount of intensification desired.Photosensitive emulsions wherein the monomer constitutes about 20% ofthe carrier material (for example, gelatin) have been found to beespecially useful. A examples of vinyl monomers contemplated to beuseful in the processes herein disclosed, mention may be made of calciumacrylate, sodium acrylate, sodium methacrylate, alkyl methacrylates,alkyl acrylates, vinylacetate, cinnamaldehyde, cinnamic acid, cinnamicalcohol, acrolein, acrylonitrile, styrene, etc. It should be understoodthat the term vinyl monomer is intended to include divinyl monomerssuch, for example, as divinylbenzene, glycol diacrylates, etc., whichwill produce a crosslinked polymer. It should be further understood thatmore than one monomer may be used, and thus a copolymer will be producedupon polymerization.

The developing step is carried out under conditions which promote theproduction of free radicals with a sufiicient lifespan to initiatepolymerization, such as the conditions conducive to color coupling.Excessively high pHs which are generally detrimental to the stability ofmost free radicals should be avoided.

The following nonlimiting examples illustrate the processes of thisinvention.

Example 1 A suspension of silver bromide crystals (average size aboutone micron) was made up in Water using a trace of glue a the stabilizer.The suspension was exposed to blue light and divided into two parts. Onepart was developed with a N p-aminophenol hydrochloride solutionbuffered at pH 8 and the other was developed with another portion of thesame solution to which was added 20%, by weight, of calcium acrylate.After about fifteen minutes the sample which contained monomer turned anintense black and a large precipitate finally settled out. The samplewithout monomer turned into a murky brown stable suspension.

Example 2 Two silver bromide gelatin emulsion plates were made up andexposed to feeble light. One plate was developed by conventional meanswith p-aminophenol and a barely perceptible image was obtained. Theother element was developed with p-aminophenol in the presence ofcalcium acrylate, with a short warming at 35 C., and an intenseblack-and-white image was obtained.

In addition to conventional photographic processes, such as describedabove, the processes of this invention are equally useful in silvertransfer processes such, for example, as those disclosed in US. PatentNo. 2,662,822. In such processes a sheet of photosensitive material,preferably a silver halide, is exposed to actinic light to createtherein a latent negative image. This latent image is developed and apositive image thereof is formed on a superposed image-receiving layer,preferably by creating between the superposed layers a uniform film of aviscous alkaline developer solution containing a substance capable offorming positive image-forming components. This latter substance, in apreferred form of the invention, comprises a silver halide solvent suchas sodium thiosulfate. With such a film of liquid composition betweenthe exposed photosensitive layer and the image-receiving layer, thedeveloper therein develops the exposed photosensitive material and thesilver halide solvent forms soluble complex ions with the unexposedphotosensitive material. These complex ions are transferred and imbibedon the image-carrying layer (which may contain silver Precipitatingagents) where they are reacted to form a positive image of the latentnegative image.

In silver transfer processes, such as described above, the processes ofthe present invention may be used to prevent staining in the highlightsof the transferred positive image. This object may be accomplished byhaving polymerizable vinyl monomers present during the development ofthe latent negative image and using the resulting polymer to at leastassist in preventing the transfer of undeveloped silver halide from suchareas. The vinyl monomer may be incorporated in the photosensitiveelement or in the developer solution.

The processesof this invention may also be used in silver transferprocesses to intensify the transferred positive image. Thisintensification may be accomplished by carrying out the reduction of thetransferred silver ions in the presence of a polymerizable vinylmonomer. The vinyl monomer may be disposed in the image-receivingelement prior to processing, or it may be imbibed from the processingsolution. When a vinyl monomer is used in the photosensitive emulsionand said monomer is soluble in the liquid processing solution, unreactedmonomer from said photosensitive element may be transferred to theimage-receiving element and used to intensify the positive image. Theresulting increased density is apparently attributable, as inconventional photography, to the aggrgating effect of the polymerproduced.

The processes of the present invention are further useful in colordiffusion transfer processes. They are especially useful in processeswherein a complete dye, soluble in aqueous alkaline solutions, isincorporated in or behind a silver halide emulsion and its transfer to asuperposed image-receiving element is controlled by reducing thepermeability of the emulsion in exposed areas. The processes of thepresent invention enable one to control the transfer of the dye bycreating in the exposed areas polymeric barriers having reducedpermeability to the dye. These barriers may be created by carrying outthe development of the latent image in the presence of a suitable vinylmonomer.

The processes of this invention are still further useful in thepreparation of relief images. Such images may be made, for example, bydeveloping a silver halide gelatin emulsion in the presence of asuitable polymerizable vinyl monomer and, after development, washing theresulting image with a material which is a solvent for the emulsion andthe monomer, but not for the resulting polymer. In certain instances,the relief images may be used as printing plates in conventionalmechanical printing processes.

Colored polymeric images can be produced by the processes of thisinvention by using a primary aromatic amino silver halide developer(i.e., a color developer) as the developing agent and carrying out thedevelopment in the presence of a color coupler in addition to the vinylmonomer. Thus, for example, a red polymeric image is produced bydeveloping exposed silver halide with a solution comprising equimolaramounts of p-aminophenol hy-- drochloride andl-(2-chloro-5-sulfophenyl)-3-methyl-5-- pyrazolone coupler and 20%, byweight, of calcium acrylate, buffered at pH 8.

Since certain changes may be made in the above product and processwithout departing from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A photographic process comprising the steps of permeating aphotosensitive element including an exposed silver halide emulsion layerwith a free radical polymerizable vinyl monomer, developing the exposedsilver halide emulsion with a benzenoid silver halide developer, whichdeveloper forms free radicals upon being oxidized as a function ofdevelopment and polymerizing said polymerizable vinyl monomer with saidfree radicals in the exposed and developed areas.

2. A photographic process as defined in claim 1 wherein said benzenoidsilver halide developer is p-aminophenol.

3. A photographic process as defined in claim 1 wherein saidpolymerizable vinyl monomer is calcium acrylate.

4. A process as defined in claim 1 wherein said silver halide developerand said polymerizable vinyl monomer are applied to the photosensitiveelement from the same processing solution.

5. A photographic process comprising the steps of developing aphotosensitive element including an exposed silver halide emulsion inthe presence of a free radical polymerizable vinyl monomer which i inthe emulsion at the time of development, with a benzenoid silver halidedeveloper, which developer forms free radicals upon being oxidized as afunction of development, polymerizing said vinyl monomer with said freeradicals in the exposed and developed areas and subsequent todevelopment washing said photosensitive element with a solvent in whichthe emulsion is soluble and the resulting polymer is insoluble toproduce a relief image.

6. A photographic process comprising the Steps of developing aphotosensitive element, including an exposed silver halide emulsionlayer, which has therein at the time of development a free radicalpolymerizable vinyl monomer, a silver halide solvent and a benzenoidsilver halide developer, which developer forms free radicals upon beingoxidized as a function of development, polymerizing said vinyl monomerwith said free radicals in exposed and developed areas, forming asoluble complex between said silver halide solvent and undevelopedsilver halide and transferring said complex to a superposedimage-receiving element to produce a transfer image on saidimage-receiving element.

7. A photographic process as defined in claim 6 wherein saidpolymerizable vinyl monomer is soluble in an aqueous alkaline processingsolution.

8. In a photographic process comprising the steps of developing aphotosensitive element including an exposed silver halide emulsion layerwith a benzenoid silver halide developer, which developer forms freeradicals upon being oxidized as a function of development, and a silverhalide solvent, and superposing said photosensitive element on animage-receiving element to produce a transfer image on saidimage-receiving element, the improvement of having a free radicalpolymerizable vinyl monomer in 6 the image-receiving element andpolymerizing said vinyl said coupler being in the silver halide emulsionat the time monomer with said free radicals in the developed areas ofdevelopment. of said image-receiving element References Cited in thefile of this patent 9. A photographic process as defined in claim 1where- UNITED STATES PATENTS in said silver halide developer is aprimary aromatic amino 0 2,380,280 Weyerts July 10, 1945 silver hahdedeveloper and the development of said ex- 2,647,056 Land July 28, 1953posed silver hallde emulsion 1s carrled out in the pres- 2 701766Hensley Feb 8 1955 ence of a color coupler in addition to saidpolymerizable 2,76O:363 palmbeck Aug 28 95 vinyl monomer to produce acolored polymeric image, 10 2,891,985 Roth Aug. 6, 1957

1. A PHOTOGRAPHIC PROCESS COMPRISING THE STEPS OF PERMEATING APHOTOSENSITIVE ELEMENT INCLUDING AN EXPOSED SILVER HALIDE EMULSION LAYERWITH A FREE RADICAL POLYMERIZABLE VINYL MONOMER, DEVELOPMENT THE EXPOSEDSILVER HALIDE EMULSION WITH A BENZENOID SILVER HALIDE DEVELOPER, WHICHDEVELOPER FORMS FREE RADICALS UPON BEING OXIDIZED AS A FUNCTION OFDEVELOPMENT AND POLYMERIZING SAID POLYMERIZABLE VINYL MONOMER WITH SAIDFREE RADICALS IN THE EXPOSED AND DEVELOPED AREAS.